logic_code.erl

%%%-------------------------------------------------------------------
%%% @author ben
%%% @copyright (C) 2017, <COMPANY>
%%% @doc
%%%
%%% @end
%%% Created : 09. mar 2017 16:02
%%%-------------------------------------------------------------------
-module(logic_code).
-author("ben").

%% API
-compile(export_all).
% 3.01 (**) Truth tables for logical expressions.
% Define predicates and/2, or/2, nand/2, nor/2, xor/2, impl/2
% and equ/2 (for logical equivalence) which succeed or
% fail according to the result of their respective operations; e.g.
% and(A,B) will succeed, if and only if both A and B succeed.
% Note that A and B can be Prolog goals (not only the constants
% true and fail).
% A logical expression in two variables can then be written in
% prefix notation, as in the following example: and(or(A,B),nand(A,B)).
%
% Now, write a predicate table/3 which prints the truth table of a
% given logical expression in two variables.
%
% Example:
% ?- table(A,B,and(A,or(A,B))).
% true  true  true
% true  fail  true
% fail  true  fail
% fail  fail  fail
%%
%%and(A,B) :- A, B.
%%
%%or(A,_) :- A.
%%or(_,B) :- B.
%%
%%equ(A,B) :- or(and(A,B), and(not(A),not(B))).
%%
%%xor(A,B) :- not(equ(A,B)).
%%
%%nor(A,B) :- not(or(A,B)).
%%
%%nand(A,B) :- not(and(A,B)).
%%
%%impl(A,B) :- or(not(A),B).
%%
%%% bind(X) :- instantiate X to be true and false successively
%%
%%bind(true).
%%bind(fail).
%%
%%table(A,B,Expr) :- bind(A), bind(B), do(A,B,Expr), fail.
%%
%%do(A,B,_) :- write(A), write('  '), write(B), write('  '), fail.
%%do(_,_,Expr) :- Expr, !, write(true), nl.
%%do(_,_,_) :- write(fail), nl.

gray(0) -> [];
gray(1) -> [[0],[1]];
gray(N) -> gray(N,for_back(gray(N-1)),[],N,0).
gray(_,[],A,_,_) -> A;
gray(0,T,A,C,S) ->
  gray(C,T,A,C,1);
gray(N,[H|T],A,C,S) ->
  gray(N-1,T,[[S|H]|A],C,S).

for_back(N) -> for_back(N,lists:reverse(N)).
for_back([],[]) -> [];
for_back([],B) -> for_back(B,[]);
for_back([H|T],B) ->
  [H|for_back(T,B)].